The mechanism of cell transformation by SV40 and polyoma virus

Establishment of a human polyclonal oral epithelial cell line

OBJECTIVE

To develop a human oral epithelial cell line to constitute a continuous source of cells readily available for human oral epithelial cell research.

STUDY DESIGN

Oral epithelial cells from a 30-week gestational, stillborn male fetus were grown in serum-free medium and transfected by lipid-mediation with the shuttle vector plasmid, pZ189, containing the T-antigen coding region and replication origin from the SV40 virus.

RESULTS

Resulting cultures produced foci of rapidly multiplying cells that failed to senesce, in contrast to controls. The transformed culture, designated GMSM-K, was polyclonal. The original culture possessed a normal human male karyotype, and the transformed line was largely hypotetraploid. Multiple clones, isolated from soft agar studies and low density plating, showed decreased doubling times. Electron microscopy and immunohistochemistry confirmed an epithelial phenotype. Cells did not generate tumors in nude mice.

CONCLUSION

Few human epithelial cell lines are available to investigators and most are tumor-derived. The nontumor-derived GMSM-K line has value as a resource for human oral epithelial cell research.

Integration of the SV40 promoter/enhancer sequences in an anchorage-independent clonal subline of SV40-infected human keratinocytes

Long-term cultures of SV40-infected human keratinocytes contain integrated, but structurally altered copies of the viral sequences. The presence of these sequences is required for expression of properties associated with the transformed phenotype including immortalization. The integrated viral sequences in an anchorage-independent line of viral-transformed human keratinocytes have been found to be contained on two BamHI fragments of about 6.9 and 5.2 kb. In the larger fragment the viral sequences were present as two tandemly repeated subgenomic fragments containing the viral origin/promoter region with nucleotide alterations that affect enhancer function, the origin of replication and T antigen binding site 1. The viral early gene promoter in one integrant gave rise to an unspliced fusion transcript comprised of a short portion of the viral early gene leader sequence and the flanking human sequences. The smaller fragment consisted of full-length SV40 containing a nine-nucleotide insertion in the C-terminal portion of the SV40 T antigen, a region involved in the regulation of viral host range.

SV40-immortalized and primary cultured human retinal pigment epithelial cells share similar patterns of cytokine-receptor expression and cytokine responsiveness

Retinal pigment epithelial (RPE) cells produce and respond to a variety of cytokines; however, molecular and biochemical studies are restricted by the limited access to large numbers of pure cells and the variability associated with different donor sources. Despite success in establishing primary human RPE (HRPE) cell cultures, the inability to sustain consistent proliferation rates and morphology over several passages remains a concern. This problem was approached by using an immortalized line of simian virus (SV)40 transformed fetal HRPE cells (SVRPE). Cytokine production, receptor expression and responsiveness in the SVRPE cell line was analyzed to determine the usefulness of this model for studying HRPE-cytokine interactions. Using reverse transcriptase polymerase chain reaction (RT-PCR), HRPE and SVRPE cells demonstrated an identical pattern of interleukin-1 receptor (IL-1R), IL-2R (alpha sub-unit), IL-6R, interferon (IFN)-gamma R and tumor necrosis factor-alpha (TNF)R p55 expression. No amplification products for TNFR p75 or granulocyte/macrophage colony stimulating factor (GM-CSF)R were demonstrated in either population. IFN-gamma stimulation induced surface human leukocyte antigen (HLA)-DR in both SVRPE and HRPE, while TNF treatment induced surface expression of intercellular adhesion molecule (ICAM)-1 on SVRPE and upregulated ICAM from basal levels on HRPE. Both cell types showed amplification products for interleukin (IL)-1 beta, IL-6 and transforming growth factor (TGF)-beta 1 using RT-PCR. The bioassays demonstrated that both populations of unstimulated cells constitutively secrete very low levels of TGF-beta and no IL-6.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of transgenic animals in the analysis of various biological aspects of normal and pathologic states

The introduction of foreign genes into the germ line of mammals has been a practical reality now for a number of years. This form of experimentation allows the creation of lines of animals tailor-made to answer specific molecular genetic questions. Manipulation of the mammalian embryos has been enormously important in developmental biology in recent years and that experience has brought about the possibility of new experiments allowing the molecular analysis of many biological processes. The methodologies involved in constructing transgenic animals have been published extensively in a number of comprehensive reviews. In typical experiments, pronuclear stage (one cell) embryos are collected after fertilization, but prior to the onset of cleavage. Exogenous cloned linearized DNA is injected into one of the two pronuclei by means of a finely drawn injection pipet. The manipulated embryo is transferred into the oviduct or ovarian bursal space of a surrogate mother previously mated with a sterile male. Alternative methods include retroviral transfection of cleavage stage embryos or insertion of genetically engineered embryo-derived embryonal stem cells into blastocysts. Offspring from these procedures are screened by standard molecular analyses to determine presence of the foreign genetic material. The present report explores the application of this methodology to a specific set of problems: (i) regulation of gene expression in vivo, (ii) the establishment of disease models for the study of pathogenesis, (iii) the use of exogenous genetic elements to correct specific genetic defects, (iv) the role of insertional mutagenesis in disruption of normal development, (v) analysis of genetic ablation, (iv) the use of transgenic animals to modulate carcinogens.

Mutants of polyomavirus middle-T antigen

Polyomavirus middle-T antigen induces the transformation of established cell lines in culture and is known to interact with and/or modulate the activity of several enzymes (pp60c.src, protein kinase C and phosphatidylinositol kinase) in vitro. This review is a compilation of the reported mutants of middle-T antigen and their biochemical and biological properties as they relate to the transformation event. The mutants of polyomavirus middle-T antigen have been previously classified phenotypically. Given the now large number of mutants, the classification presented here is based upon the position within the molecule. A model of middle-T is presented in which the protein is considered as consisting of three domains: a hydrophobic domain (the putative membrane-binding domain), the amino-terminal half of the molecule (the putative pp60c.src-binding domain) and the intervening amino acids (the putative modulatory domain). A current model for the induction of transformation by polyomavirus middle-T is presented.

Tumour prevention and rejection with recombinant vaccinia

Tumour-specific antigens (TSA; ref. 1) have been exploited in the diagnosis and imaging of human cancer and anti-TSA antibodies have therapeutic potential. Vaccination with TSA or anti-idiotypic (TSA) antibodies has also been used to control tumour growth in model systems. An effective immune response nevertheless demands copresentation of antigen with host histocompatibility determinants. We therefore examined whether live vaccinia virus recombinants expressing TSA in cells of the vaccinated host might better elicit tumour immunity. Polyoma virus (PY) is tumorigenic in rodents; because killed PY-transformed cells can elicit tumour immunity, a PY-specific TSA has been postulated. Tumorigenesis involves expression of three early PY proteins, large-T (LT), middle-T (MT) and small-T (ST), but their role as TSAs is unclear. We therefore expressed the three T proteins in separate vaccinia recombinants. Rejection of PY tumours was observed in rats immunized with recombinants expressing either LT or MT. Further, tumour-bearing animals could be induced to reject their tumours by inoculation of recombinants.

Transformation of DNA repair-deficient human diploid fibroblasts with a simian virus 40 plasmid

Fibroblasts from patients with xeroderma pigmentosum (XP) complementation groups A, C, D, E, and G, as well as Bloom syndrome (BS) and Fanconi anemia (FA) have been transfected with a plasmid, pSV7, containing the early region of Simian virus 40 (SV40). All of the cultures exhibited cytologic changes characteristic of transformed cells and expressed T-antigen. They also contained integrated copies of DNA derived from the vector, and in several cases, extrachromosomally replicated DNA. Not all of the transfected cultures became immortalized. The transformed xeroderma pigmentosum (XP) cultures retained their UV-sensitive phenotype in all but one case. The BS and FA cell lines retained their characteristic phenotype. All of the cultures, except the BS cells, can be readily transfected with the plasmids, pSV2neo and pSV2gpt.

Calcium, cyclic AMP and protein kinase C--partners in mitogenesis

Evidence is steadily mounting that the proto-oncogenes, whose products organize and start the programs that drive normal eukaryotic cells through their chromosome replication/mitosis cycles, are transiently stimulated by sequential signals from a multi-purpose, receptor-operated mechanism (consisting of internal surges of Ca2+ and bursts of protein kinase C activity resulting from phosphatidylinositol 4,5-bisphosphate breakdown and the opening of membrane Ca2+ channels induced by receptor-associated tyrosine-protein kinase activity) and bursts of cyclic AMP-dependent kinase activity. The bypassing or subversion of the receptor-operated Ca2+/phospholipid breakdown/protein kinase C signalling mechanism is probably the basis of the freeing of cell proliferation from external controls that characterizes all neoplastic transformations.